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  2. Transformation matrix - Wikipedia

    en.wikipedia.org/wiki/Transformation_matrix

    A reflection about a line or plane that does not go through the origin is not a linear transformation — it is an affine transformation — as a 4×4 affine transformation matrix, it can be expressed as follows (assuming the normal is a unit vector): [′ ′ ′] = [] [] where = for some point on the plane, or equivalently, + + + =.

  3. Rotation matrix - Wikipedia

    en.wikipedia.org/wiki/Rotation_matrix

    A more direct method, however, is to simply calculate the trace: the sum of the diagonal elements of the rotation matrix. Care should be taken to select the right sign for the angle θ to match the chosen axis: ⁡ = + ⁡, from which follows that the angle's absolute value is

  4. Sigmoid function - Wikipedia

    en.wikipedia.org/wiki/Sigmoid_function

    This function is unusual because it actually attains the limiting values of -1 and 1 within a finite range, meaning that its value is constant at -1 for all and at 1 for all . Nonetheless, it is smooth (infinitely differentiable, C ∞ {\displaystyle C^{\infty }} ) everywhere , including at x = ± 1 {\displaystyle x=\pm 1} .

  5. Change of variables - Wikipedia

    en.wikipedia.org/wiki/Change_of_variables

    The map is called a regular coordinate transformation or regular variable substitution, where regular refers to the -ness of . Usually one will write x = Φ ( y ) {\displaystyle x=\Phi (y)} to indicate the replacement of the variable x {\displaystyle x} by the variable y {\displaystyle y} by substituting the value of Φ {\displaystyle \Phi } in ...

  6. Eigenvalues and eigenvectors - Wikipedia

    en.wikipedia.org/wiki/Eigenvalues_and_eigenvectors

    The corresponding eigenvalue, characteristic value, or characteristic root is the multiplying factor (possibly negative). Geometrically, vectors are multi-dimensional quantities with magnitude and direction, often pictured as arrows. A linear transformation rotates, stretches, or shears the vectors upon which it acts. Its eigenvectors are those ...

  7. DFT matrix - Wikipedia

    en.wikipedia.org/wiki/DFT_matrix

    An N-point DFT is expressed as the multiplication =, where is the original input signal, is the N-by-N square DFT matrix, and is the DFT of the signal.. The transformation matrix can be defined as = (), =, …,, or equivalently:

  8. Transformation (function) - Wikipedia

    en.wikipedia.org/wiki/Transformation_(function)

    In mathematics, a transformation, transform, or self-map [1] is a function f, usually with some geometrical underpinning, that maps a set X to itself, i.e. f: X → X. [ 2 ] [ 3 ] [ 4 ] Examples include linear transformations of vector spaces and geometric transformations , which include projective transformations , affine transformations , and ...

  9. Singular value decomposition - Wikipedia

    en.wikipedia.org/wiki/Singular_value_decomposition

    The SVD decomposes M into three simple transformations: an initial rotation V ⁎, a scaling along the coordinate axes, and a final rotation U. The lengths σ 1 and σ 2 of the semi-axes of the ellipse are the singular values of M, namely Σ 1,1 and Σ 2,2.